This study set out to evaluate the acquisition of immunologic function in infants and children with DiGeorge syndrome. In this syndrome, children are born with insuficient thymic tissue to support normal T cell development. This study is designed to document the dynamic nature of the immunologic development in this patient population. Laboratory evaluations of T cell production and T cell function in infancy have characterized the acquisition of T cell function. A cohort of older children have had single time point evaluations of T cell production, T cell function, and B cell function. Studies to date on 300 children and adults (of whom 51 were supported through the GCRC) have revealed less immunologic improvement in the first year of life than was thought to occur (Sullivan, KE, et al., Clin. Diag. Lab. Immunol. 6:906-911, 1999) Another study is in preparation and reveals possible premature senescence in this population. In the next year, we will focus on recruiting older patients with chromosome 22q11.2 deletion syndrome into the study because there is a paucity of knowledge about this group. Our initial studies have suggested premature immunologic senescence in chromosome 22q11.2 deletion syndrome. Characterstic findings included inversion of CD4/45RA to CD4/45RO ratio, lymphopenia, and decreased proliferative responses. These are all typicaly seen in normal controls over the age of 50. The significance of these findings is uncertain. Senescence in normals is associated with decreased ability to respond to immunizations and difficulty in controlling infections. If this turns out to be true for this relatively chronologically young population, one would expect a signficant healthcare burden as a result.